If you take each 3x3 game grid and flatten it to a string of nine characters, this can be solved with a regexp. This particular method of solving it wasn't really touched upon in (Golf) Tic Tac Toe, but works great. The conversion of a 3x3 grid to a single flat string is trivial, so I'll just demonstrate the regexp portion of the solution.

The regexp can be expressed in a way that tests for one of four conditions. I started out with a slightly more complex regexp, and then was able to see the forest through the trees, and found a way to boil it down to this common denominator.

In the following snippet, I never placed any 'o's because I wanted to keep it visually clear what was going on. The hyphens could be replaced with x's and o's as though a real game were being played, and the regexp will discover whether X or O wins. I just wanted to show each of the winning possibilities, so I used hyphens to isolate X.

Here's the code:

use strict;
use warnings;

# Assume that the 3x3 AoA has been flattened to a single string.
# Each string, therefore, equates to a single game.

my @games = (   "x---x---x",    # Diag from top left. 1
                "--x-x-x--",    # Diag from top right. 3
                "x--x--x--",    # Vert from top left. 2
                "xxx------",    # Horiz from top left. 4
                "---xxx---",    # Horiz from mid left. 4
                "------xxx",    # Horiz from bottom left. 4
                "-x--x--x-",    # Vert from top mid. 2
                "--x--x--x"  );
            

my $i;
foreach my $game ( @games ) {
    print "Game ", ++$i, "\t";
    if ( $game =~ m/ 
                    ([xo])
                    (?:
                         (?:...\1){2}
                      |  (?:..\1){2}
                      |  (?:.\1){2}
                      |  \1{2}(?=(?:...){0,2}$)
                    )
                   /ix ){
        print "$1 wins.\n";
    } else {
        print "no winner\n";
    }
}
[download]

Update:
Here's a golfier version that uses the same solution technique:

print m/([xo])((...\1){2}|(..\1){2}|(.\1){2}|\1{2}(?=(...){0,2}$))/i?
"$1 wins.\n":"No winner.\n" foreach qw/x---x---x --x-x-x-- x--x--x-- 
xxx------ ---xxx--- ------xxx -x--x--x- --x--x--x x---x-x--/;
[download]

Update2: Fixed a problem that would allow misaligned 3-in-a-rows to win when they shouldn't.